Macro Lens Configurations

Since I enjoy macro photography, I wanted to create an easily referenced
list of which of my lens and accessory combinations will provide what
magnification factor and at what focusing distance. Not all combinations
have the same image quality; I'll try to post example photos when possible.

In the table below, the magnification factor indicates the ratio of an
object's actual size to the size at which it is rendered on the imagine
sensor (which is 22.2mm or 7/8" wide on a Canon XTi/400D). Numbers marked in
green are greater than 1:1
(1.0x), or larger than life size. At 1:1, a 10mm object will be rendered
at 10mm on the image sensor, filling nearly half the frame. This is what
you need for portraits of bugs or similar objects. Numbers marked in
yellow are greater than 1:2
(0.5x), or half life
size. At 1:2, a 10mm object will be rendered at 5mm on the image sensor,
filling about a quarter of the frame. This is still a respectable
magnification for flowers or other small objects. The listed magnification
is always achieved at the minimum focusing distance, of course. Working
distances here are always listed from the front end of the lens.

One useful method for improving magnification is to mount a wide angle
lens in reverse, either directly to the body or to the end of another
lens. Special adapters are available to make these attachments. To
reverse mount a lens directly to the body, the adapter has an EOS mount
on one side and filter threads on the other side. You simply screw the
adapter onto the lens' filter threads, and then mount the assembly in
reverse on your camera body. If you want to stop down the lens below
the maximum aperture (and you will), you'll need to use an older lens
with a manual aperture control ring. Wider angle lenses give larger
magnifications. My 50mm lens provides about 1:1.3 at about 4". The
range of working distance is extremely small--only about 1/2" from
the min to max distance.

Mounting a second lens to the end of your main lens works similarly.
The adapter simply has filter threads on both sides, and both lenses
screw to it. The second lens is always used wide open, so manual
aperture rings are not necessary here. However, the wider the aperture,
the more light will be available to your primary lens. The magnification
achieved is the focal length of the first (forward) lens divided by
the focal length of the second (reversed) lens. A 50mm lens mounted
to the end of a 100mm lens will give 2x magnification. A 50mm mounted
on a 300mm lens will give 6x magnification, which will completely fill
the frame with the head of a butterfly. Depth of field is razor thin
at these magnifications (a fraction of a millimeter at f/32), so you'll
have to stop down the primary lens quite a ways to show any detail.
Using a flash is nearly mandatory.

Extension tubes are just spacers placed between your camera
body and the lens. Longer tubes allow a lens to focus more closely
than it otherwise could. Both the minimum and maximum distance are
affected, so you'll lose infinity focus when using tubes. They also
reduce the amount of light that makes it to the sensor. Moving the
lens closer to the subject naturally makes the object appear bigger.
This affect is more pronounced on wider-angle lenses, as evidenced
by the change in magnification values for the 50mm and 135mm lenses
in the table below.

Diopters are essentially just magnifying glasses attached to the
filter threads on the end of your lens. I'm a little fuzzy on how
they do their thing, but they also reduce the focusing distance.
Diopters are more effective on longer focal length lenses. Again,
compare the results for the 50mm and 135mm lenses in the table below.
Diopters can be stacked on top of each other to combine their strength,
so a +2 stacked on a +3 will yield the same magnification as a +5
(and relatively low image quality).

NOTE: I've acquired quite a number of new lenses since I last
updated this list, so it's now far from exhaustive. Someday I should
take the time to bring this up to date.

Lens

Focal Length

Ext. Tubes

Front Attachments

Mag.

Min Dist.

Max Dist.

Sigma 17-70 f/2.8-4.5 DC MACRO

17mm

~2"

inf

70mm

0.43x

0.5"

inf

Asahi/Pentax Super-Tak 50/1.4

50mm

0.14x

~18"

inf

+2 diopter

0.25x

+3 diopter

0.30x

+2 & +3 diopters

0.39x

11mm

0.36x

22mm

0.61x

~4"

64mm

>1x

22mm

+2 diopter

0.70x

~3.5"

22mm

+3 diopter

0.74x

~3"

22mm

+2 & +3 diopters

0.83x

~3"

Asahi/Pentax Super-Tak 50/1.4

50mm reversed

0.78x

~4"

Micro-Nikkor 55/2.8 AIS

55mm

0.51x

~4"

inf

29mm

1.00x

64mm

1.69x

~1.5"

~2.5"

Tamron 90/2.5 macro (52B)

90mm

0.50x

~9"

inf

Asahi/Pentax Super-Tak 135/3.5

135mm

0.11x

~60"

inf

+2 diopter

0.40x

+3 diopter

0.56x

+2 & +3 diopters

0.89x

11mm

0.19x

22mm

0.28x

64mm

0.56x

~18"

~18"

22mm

+2 diopter

0.62x

22mm

+3 diopter

0.93x

22mm

+2 & +3 diopters

1.17x

50/1.4 lens

2.70x

Canon 70-300 f/4-5.6 IS

70mm

inf

300mm

~54"

inf

70mm

50/1.4 lens

1.40x

~1.25"

~1.75"

300mm

50/1.4 lens

6.00x

Opteka 500/8

500mm

~400"

inf

64mm

0.20x

~120"

~180"

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